Rowan Baxter rejected an offer to share custody of his children, aged three to six, with his estranged wife Hannah Clarke before he killed them all in a horrific car fire.
Ms Clarke, 31, and her kids Aaliyah, six, Laianah, four, and Trey, three, burned to death after Baxter, 42, set the Kia Sportage on fire on Wednesday morning.
Prior to the murder-suicide, Baxter ignored his lawyer's advice to accept an offer that allowed him to have custody of the three children 165 days of the year, it was revealed on Saturday.
A source close to Baxter told the ABC that the killer would alternate between three days and four days of custody per week if he accepted the deal.
'He got the children back but... he wanted 50-50, that was it. It was his way or nothing,' he told the national broadcaster.
'In my view, it wasn't about the children at all, he just couldn't move past the relationship with Hannah.'
Rowan Baxter, 42, rejected an offer to share custody of his children, aged three to six, with his estranged wife Hannah Clarke before he killed them all in a horrific car fire
Hannah Clarke (pictured with children Trey, Aaliyah and Laianah) was murdered by her estranged husband on Wednesday
Baxter allegedly kidnapped his six-year-old daughter on Boxing Day last year, which allowed the Ms Clarke to get a domestic violence order (DVO) against him.
In January, the DVO was varied and Baxter regained access to his children, which is when he refused to sign the consent form that would give him 165 days of custody per year during mediation, according to the source.
The father instead signed non-legally binding parenting agreement that gave him the same level of access as Ms Clarke - but the agreement was voided when he allegedly assaulted his wife in breach of the DVO.
On Wednesday, Baxter rushed into his estranged wife's car, put a knife to her throat and told her to drive, then set her on fire with their three children when she stopped for help.
Her shattered father Lloyd Clarke has pieced together the horrific timeline of events that led to the tragic loss of four lives and Baxter's suicide.
Despite suffering burns to 97 per cent of her body, heroic Hannah was able to give police at the scene a detailed statement about what happened.
Lloyd Clarke (pictured, left, with his grandson Trey) was a hands-on grandpa to Hannah's three children
She was taking the children to school after 8am from her parents' house in Camp Hill, Brisbane, while her killer lay in wait.
A notorious control freak, Baxter had been spiralling since Hannah left him with the kids in November and decided to get his revenge.
'Rowan must have been lurking somewhere close, either hidden around the side of the house or in the neighbour's driveway,' Mr Clarke told Daily Mail Australia.
'His car was found down the street, this was definitely premeditated.'
Hannah got the children into the car and walked to the back seat to buckle Trey's seatbelt as the girls could do their own.
That was all the time her killer needed.
'He was very quick, being an ex-athlete. So as she's doing that, he's run into the passenger seat and held a knife to her throat and told her to drive,' Mr Clarke said.
'She got down to the corner here, turned left, and saw a neighbour washing his car and drove towards him to get help.'
A shrine grows at the scene where Hannah and her three kids were doused in fuel and set alight, while one person leaves a poignant sign about domestic violence (pictured)
The shocking murder-suicide that has left Australia reeling unfolded just metres from the home of Ms Clarke's parents on Raven Street, Camp Hill, as she drove her children to school
Hannah Clarke (pictured with her three children, aliyah, 6, Laianah, 4, and Trey, 3) died of her injuries on Wednesday
Michael Zemek was the heroic first responder to the horror that was about to engulf Raven Street and traumatise dozens of residents.
As Hannah stopped alongside him and yelled 'he's poured petrol on me', Baxter realised his time was up, and lit the fire while he was still inside the car.
'When he gets trapped in a corner, he has no empathy so he would have just gone ''ok, that's it, light it, boom, gone'',' Mr Clarke said.
'In a way I hope he poured it (the petrol) on the girls because that would have been quicker.'
As the car was engulfed in flames, Hannah jumped out while her activewear was on fire and the flaming petrol melting her skin.
Mr Zemek helped her smother the flames by dropping to the ground and rolling, then sprayed water on her horrific burns with his garden hose.
He suffered burns to his face and hands in the process and is still recovering in hospital.
Hannah Clarke (pictured with her three children, aliyah, 6, Laianah, 4, and Trey, 3) is seen enjoying a day with her own grandmother (far left)
Left: Hannah Clarke pictured with her 'main man', son Trey in a beach